Electoral rules should affect parliamentary behavior. In particular, deputies elected from single-member districts should be more likely to deviate from the party line than deputies elected under proportional representation. This paper suggests a framework for conceptualizing and modeling the effect of the type of mandate on deputies’ propensity to cast deviating votes in mixed electoral systems. The proposed modeling strategy uses disaggregated voting data and integrates dependencies among observations in a multi-level design. Empirically, the paper analyses voting behavior in the 16th German Bundestag (2005–2009) and shows that the odds of district MPs to deviate are significantly higher despite frequent claims that the two types of MPs behave alike. However, the behavioral differences cannot be attributed to attempts by district MPs to follow their local constituents as competing principals.
